A modern television receiver is used for much more than receiving broadcast signals. For example, a television receiver is often used as an audio and video display with peripheral equipment such as VCRs, video games, home computers and video disk players. Some equipment, such as the VCR, includes a full complement of functions. A VCR includes a UHF/VHF television tuner which enables it to receive both UHF and VHF television channel frequencies and has internal radio frequency (RF) switches to permit recording of one channel frequency signal while viewing another on a television receiver. The VCR also has a signal modulator for taking its recorded information from tape and modulating it onto a particular channel frequency, generally that corresponding to VHF channels 3 or 4, for viewing on the television receiver. Most VCRs also incorporate a timer that may be set or programmed to record different channels at different times. The limits on recording capability are determined by the length of recording tape available and, indeed some VCRs have a "magazine" system for automatically changing tapes. Thus the possibilities of the VCR for so-called "time shifting" purposes, that is for recording programs for viewing at a later, more convenient time, are almost limitless.
Equally important in the field of video information dissemination, has been the rise of cable systems. In these systems a subscriber is supplied, by means of a cable, with a very large number of television channels including one or more "pay" channels that are scrambled and viewable with a decoder obtained by paying an additional prescribed fee. Unfortunately these developments have tended to negate many of the features of the VCR.
In a conventional installation, the VCR is connected to the output of the cable converter/decoder. The single output of the converter/decoder is a modulated RF carrier corresponding to channel 3/4. Therefore the tuning capability of the VCR is useless since the output of the converter/decoder corresponds to a single television channel frequency. Additionally the VCR feature of being able to record one program while watching another is lost. Similar problems exist when special over-the-air television signal descramblers are used with VCRs and non-cable-connected television receivers. This problem has given rise to a number of solutions to enable a VCR to record a pay TV channel, for example, while the subscriber is viewing a conventional channel. All of these solutions require a number of RF switches which must be manually operated to provide the proper signal paths. However since manual switching is required, these solutions still limit the capabilities of the VCR to automatically record different programs (channels) at different times of the day. Needless to say, the complexity involved in correctly arranging the various switches has proven extremely burdensome, if not impossible, for many users. Accordingly, there is a need in the art for a simple system that will enable a VCR to be fully used in any cable system or in an over-the-air system employing a decoder.